A metamaterial cell and metamaterial structure based on independent chiral twist units

Abstract

The present invention discloses a metamaterial cell and metamaterial structure based on independent chiral twist units. The metamaterial cell comprises two mirror-symmetrical chiral units. The chiral units comprise two toruses and a plurality of elastic rods. The two toruses are coaxially spaced apart, and the elastic rods are periodically connected between the two toruses along the circumference of the toruses. Within the same chiral unit, when the chiral unit is free of external load, the elastic rods are in an inclined state, and the inclination direction and inclination angle of each elastic rod are the same. The two mirror-symmetrical chiral units share a torus, or a pair of toruses within the two mirror-symmetrical chiral units are coaxially fixedly connected. The present invention is applied to the field of metamaterial structures and exhibits high static stiffness, high load-bearing buckling strength, large ultimate strain, and high elastic strain energy density. Compared to existing lattice structures composed of the same primitives, under the same substrate strength constraint, the equivalent modulus within a small deformation range is comparable, and the load-bearing buckling strength and elastic strain energy density are significantly improved.

Description

Technical Field

[0001] The present invention relates to the fields of mechanical engineering, shipbuilding and oceanography, vibration and noise control, structural impact resistance, and metamaterial structure technology. Specifically, it relates to a metamaterial cell and metamaterial structure based on independent chiral twist units, which can provide high static stiffness, high load-bearing buckling strength, and high elastic strain energy density. The metamaterial cell and metamaterial structure can be widely used in the structural load-bearing, impact resistance, energy absorption, elastic energy storage, and vibration control of mechanical structures. Background Art

[0002] Materials and structures with high elastic energy storage density hold great promise for applications in a wide range of fields, including energy storage, high load-bearing capacity, high impact resistance, and agile motion. However, achieving this goal requires materials or structures that simultaneously possess high modulus, high strength, and the ability to withstand large deformations. While this can be achieved at the microscale using high-strength materials such as carbon nanotubes, achieving this goal at the macroscale presents significant challenges and remains elusive.

[0003] Mechanical / mechanical metamaterial structures refer to artificial materials with extraordinary mechanical properties, which can produce characteristics such as low density and high modulus, negative Poisson's ratio, and elastic wave control. Typical structures include two-dimensional honeycomb structures, three-dimensional lattice structures, and folded structures. In particular, lattice metamaterial structures with lightweight, high stiffness, and high strength have been widely used, providing important structural design solutions for industrial systems such as aviation, aerospace, shipbuilding, high-speed rail, and automobiles. However, the buckling of existing metamaterial structures under compressive load is dominated by the bending buckling of the elementary rod structure. Under the limited material strength limit, the buckling platform stress is inconsistent with its overall ultimate strain, which limits the ultimate elastic energy storage capacity. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a metamaterial cell and metamaterial structure based on independent chiral twist units, which have high static stiffness, high load-bearing flexural strength, large ultimate strain and high elastic strain energy density. Compared with the existing lattice structure composed of the same primitives, under the same substrate strength constraint, its equivalent modulus within a small deformation range is equivalent, the load-bearing flexural strength is increased by 5-10 times, and the elastic strain energy density is increased by more than 5-20 times.

[0005] To achieve the above-mentioned object, the present invention provides a metamaterial cell based on independent chiral twist units, comprising two mirror-symmetrical chiral units;

[0006] The chiral unit includes two annular surfaces and a plurality of elastic rods, the two annular surfaces are coaxially arranged and spaced apart, and the elastic rods are periodically distributed between the two annular surfaces along the circumference of the annular surfaces;

[0007] In the same chiral unit, when the chiral unit has no external load, the elastic rods are in an inclined state, and the inclination direction and inclination angle of each elastic rod are the same;

[0008] The two mirror-symmetrical chiral units share one annular surface, or a pair of annular surfaces in the two mirror-symmetrical chiral units are coaxially fixedly connected.

[0009] In one embodiment, in the same chiral unit:

[0010] The first end of the elastic rod is fixedly connected to one of the annular surfaces, and the distance between the center of the first end of the elastic rod and the center of the corresponding annular surface is a first pitch circle radius R1;

[0011] The second end of the elastic rod is fixedly connected to another annular surface, and the distance between the center of the second end of the elastic rod and the center of the corresponding annular surface is a second pitch circle radius R2;

[0012] Wherein, R1=R2=R, and R is the installation pitch radius of the elastic rod between the two annular surfaces.

[0013] In one embodiment, in the same chiral unit, the distance between two ring surfaces is h0, and h0≈4R~6R.

[0014] In one embodiment, the elastic rod is a cylindrical structure that can withstand large deformations such as compression, bending and torsion, including but not limited to soft rubber rods, coil springs, steel wire ropes, carbon nanotubes, and fiber-reinforced rods.

[0015] In one embodiment, in the same chiral unit, the distance between two adjacent elastic rods is greater than or equal to the diameter of the elastic rod.

[0016] To achieve the above object, the present invention further provides a metamaterial structure based on independent chiral twist units, comprising a plurality of the above metamaterial cells;

[0017] The metamaterial cells are distributed in a two-dimensional planar array, a three-dimensional multi-layer array or a three-dimensional skeleton structure.

[0018] In one embodiment, when the metamaterial cells are distributed in a two-dimensional planar array:

[0019] The metamaterial cells are arrayed on a two-dimensional plane to form a single-layer metamaterial structure, and the annular surfaces located at the top and bottom layers of the single-layer metamaterial structure are respectively fixed or integrally formed on the same flat plate, but the central annular surfaces of the metamaterial cells are independent of each other.

[0020] In one embodiment, when the metamaterial cells are distributed in a three-dimensional multi-layer array, the metamaterial structure is formed by stacking a plurality of single-layer metamaterial structures in a vertical direction.

[0021] In one embodiment, when the metamaterial cells are distributed in a three-dimensional skeleton configuration, the metamaterial cells are connected to form a spatial skeleton of a polyhedral structure, and the nodes of the spatial skeleton are block structures.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] 1. The present invention utilizes layered chiral units to form metamaterial cells. When a metamaterial structure is composed of a metamaterial cell array, the present invention not only maintains comparable stiffness (i.e., equivalent modulus) within a small deformation range to existing high-rigidity metamaterial structures such as rhombus and octahedron lattices with the same equivalent density, but also significantly outperforms existing high-rigidity metamaterial structures in terms of overall buckling strength and elastic energy storage density. The metamaterial structure has the advantages of high static stiffness, high load-bearing buckling strength, large ultimate strain, and high elastic strain energy density.

[0024] 2. The elastic rod in the present invention can be directly prepared from materials or structures that can withstand large deformation, such as metal springs. It not only has high environmental adaptability and mature preparation technology, but also can maintain excellent elastic deformation recovery under large deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0026] Figure 1 Schematic diagram of the structure of the metamaterial cell in Example 1 of the present invention;

[0027] Figure 2 Schematic diagram of the structure of the chiral unit in Example 1 of the present invention;

[0028] Figure 3 Schematic diagram of the torsional buckling deformation mode of the metamaterial cell under axial compression in Example 1 of the present invention;

[0029] Figure 4 Schematic diagram of the structure of a two-dimensional single-layer chiral metamaterial structure array in Example 2 of the present invention;

[0030] Figure 5 Schematic diagram of the structure of a three-dimensional multi-layer chiral metamaterial structure array in Example 2 of the present invention;

[0031] Figure 6 Schematic diagram of the structure of the three-dimensional skeleton chiral metamaterial structure array in Example 2 of the present invention;

[0032] Figure 7 Schematic diagram of metamaterial structures of different configurations made of the same elastic rods in an embodiment of the present invention, wherein: Figure 7 (a) is a schematic diagram of the chiral lattice. Figure 7 (b) is a simplified schematic diagram of the octahedron lattice. Figure 7 (c) is a simple schematic diagram of the diamond lattice. Figure 7 (d) is a brief schematic diagram of the stretched overall lattice;

[0033] Figure 8 Graphs showing equivalent stress-strain curves of metamaterial structures of different configurations made of the same elastic rods in an embodiment of the present invention;

[0034] Figure 9 Graphs showing the performance of different metamaterial arrays composed of uniform solid elastic rods in an embodiment of the present invention are shown below: Figure 9 (a) is the normalized mass density-Young's modulus curve, Figure 9 (b) is the equivalent ultimate strain and normalized equivalent buckling strength curve for a given elastic rod strength. Figure 9 (c) is the equivalent ultimate strain and normalized elastic strain energy density curve for a given elastic rod strength;

[0035] Figure 10 : This is a performance curve diagram of a diamond lattice composed of metal springs and a chiral metamaterial array in an example of an embodiment of the present invention, wherein: Figure 10 (a) is the curve of equivalent ultimate strain and equivalent buckling strength. Figure 10 (b) is the curve of equivalent ultimate strain and elastic strain energy density.

[0036] Reference numerals: torus 1, elastic rod 2.

[0037] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0039] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0040] Example 1

[0041] like Figure 1 The figure shows a metamaterial cell based on independent chiral twisting units disclosed in this embodiment (hereinafter referred to as "metamaterial cell"). The metamaterial cell includes chiral units with the same structure, and the two chiral units are distributed in a mirror-symmetrical manner.

[0042] refer to Figure 2 The chiral unit is cylindrical in shape and consists of two toruses 1 and several elastic rods. The toruses 1 can be circular or annular plates. The two toruses 1 are spaced apart vertically and coaxially, with the minimum distance between them maintained at h0. The elastic rods 2 are periodically connected between the two toruses 1 along the circumference of the toruses 1. Initially, in the absence of external load, the upper and lower toruses 1 of the chiral unit have an initial relative helical angle α0 that is not equal to zero. That is, within the same chiral unit, when the chiral unit is unloaded, the elastic rods 2 are tilted, and the tilt direction and tilt angle of each elastic rod 2 are identical, thus forming chiral properties.

[0043] In the same metamaterial cell, two mirror-symmetrical groups of chiral units can either share a torus 1, or a pair of torus 1 close to each other in the two groups of chiral units can be coaxially fixed together by gluing, snap-fit ​​connection, screw fixation, welding, etc. Under the action of external compressive load, the two torus 1 at the two ends of the metamaterial cell remain fixed, while the middle torus 1 rotates and drives the internal elastic rod 2 to twist. When the compressive load is large, the elastic rod 2 will bend, forming a chiral distortion deformation as a whole, while the free chiral distortion deformation will not generate torque at the boundaries at both ends, that is, Figure 3 shown.

[0044] In the same chiral unit, the first end of the elastic rod 2 is fixedly connected to one of the torus surfaces 1 by gluing, riveting, welding, or the like, or is integrally formed by 3D printing, and the distance between the center of the first end of the elastic rod 2 and the center of the corresponding torus surface 1 is a first pitch radius R1. The second end of the elastic rod 2 is fixedly connected to the other torus surface 1 by gluing, riveting, welding, or the like, or is integrally formed by 3D printing, and the distance between the center of the second end of the elastic rod 2 and the center of the corresponding torus surface 1 is a second pitch radius R2. Metamaterials with parameters R1≠R2 have lower performance than metamaterials with R1=R2. Therefore, in this embodiment, R1=R2=R is preferably set, where R is the installation pitch radius of the elastic rod 2 between the two torus surfaces 1. That is, the periodically distributed elastic rods 2 in the same chiral unit do not form a conical platform as a whole, but rather a cylinder.

[0045] In specific applications, for a given torus spacing h0 and overall buckling strain, reducing the installation pitch radius R of the elastic rod 2 between the two toruses 1 and the initial relative helical angle α0 of the toruses 1 can improve the elastic energy storage density and load-bearing strength of the chiral metamaterial structure, with the performance improvement brought about by reducing R being more significant. Therefore, to ensure overall structural stability, in this embodiment, the spacing of the toruses 1 is preferably set to h0 ≈ 4R-6R, for example, h0 = 30mm and R = 7.5mm.

[0046] In this embodiment, the elastic rod 2 is a cylindrical structure capable of withstanding flexure and torsional deformation, such as a rubber rod, metal spring, steel wire rope, carbon nanotube, or fiber-reinforced rod. Furthermore, to ensure that the deformed elastic rods 2 in the chiral unit do not contact each other before the structure collapses, the spacing between two adjacent elastic rods 2 in the same chiral unit is set to be greater than or equal to the diameter of the elastic rod 2.

[0047] Example 2

[0048] This embodiment discloses a metamaterial structure based on independent chiral twist units (hereinafter referred to as the "metamaterial structure"), which primarily comprises the metamaterial cells of Example 1, each metamaterial cell being arranged in a two-dimensional planar array, a three-dimensional multilayer array, or a three-dimensional skeleton configuration. The two-dimensional single-layer array and the three-dimensional multilayer array can provide higher energy storage density and higher buckling resistance.

[0049] refer to Figure 4 When the metamaterial cells are distributed in a two-dimensional planar array, they are arranged on the two-dimensional plane to form a single-layer metamaterial structure. The torus surfaces at the top and bottom of the single-layer metamaterial structure are fixed to or integrally formed on the same plane, but the central torus surfaces of the metamaterial cells are independent of each other. Preferably, the two-dimensional array lattice in the single-layer metamaterial structure is square or diamond-shaped, and the distance between the metamaterial cells is as small as possible without mutual interference.

[0050] refer to Figure 5 When the metamaterial cells are distributed in a three-dimensional multi-layer array, the metamaterial structure consists of multiple Figure 4 The single-layer metamaterial structure shown is stacked in a vertical direction, and two adjacent single-layer metamaterial structures are fixed by gluing.

[0051] refer to Figure 6 When the metamaterial cells are arranged in a three-dimensional skeleton configuration, they connect to form a polyhedral spatial skeleton. The spatial skeleton can be configured as a cube, rhombus, octahedron, dodecahedron, or other shapes, with a cube being the preferred configuration in this embodiment. The nodes of the spatial skeleton are block-shaped skeleton node blocks, whose dimensions are comparable to the torus surfaces at the ends of the chiral units. The chiral cells are fixedly connected to the skeleton node blocks at their ends.

[0052] The metamaterial structure based on the independent chiral twisting unit in this embodiment is further described below with reference to two groups of specific performance comparison examples with existing metamaterial structures.

[0053] In Example 1, all metamaterial structures are composed of uniform elastic rods with a radius of r = 1.5 mm and a length of L0 = 30 mm. The Young's modulus of the elastic rod is E s , assuming its intensity is σ v =0.2Es, the example uses dimensionless normalized performance indicators for comparison.

[0054] refer to Figure 7 , the existing octahedral lattice, rhombus lattice, stretched integral lattice and the chiral lattice of this embodiment (specifically Figure 4 The performance of the single-layer metamaterial structure shown in the figure is compared in simulation. The tensile lattice is composed of a regular tetradecahedron with tension and compression rods added inside. The initial parameters of the chiral lattice are h0 = 30 mm, R = 7.5 mm, and α0 = 5°. The equivalent compressive stress-strain curves of different metamaterial structures prepared from the same hard rubber are shown in Figure 2. Figure 8 As shown in Figure 2, nonlinear finite element methods are used to perform numerical calculations on different metamaterial models. During the calculations, compressive loads are applied to different models to cause the metamaterial structure to produce the required compressive buckling deformation. limit The maximum Mises stress in the rod of the metamaterial reaches the strength σ v The global equivalent compressive strain of σ is larger, and the higher the deformation resistance is. bk for Figure 8 In the compression buckling curve of the metamaterial structure shown in the figure, the global equivalent stress at the buckling platform stage is larger, indicating that the buckling bearing strength of the metamaterial structure is higher. ɸ is the stress of the metamaterial structure when the local stress reaches σ v (corresponding to global strain reaching ɛ limit). E is the equivalent Young's modulus of the metamaterial under small strain.

[0055] like Figure 9 As shown in Example 1, the properties of chiral metamaterials with different parameters are calculated, and experimental tests are completed under typical parameters, such as Figure 8 As shown. Both simulation and experimental test results show that:

[0056] 1. Compared with existing high-rigidity metamaterial structures such as rhombus and octahedral lattices of the same equivalent density, the layered array chiral metamaterial structure proposed in this embodiment has a stiffness (i.e., equivalent modulus) comparable to that of existing metamaterials within a small deformation range, indicating high stiffness.

[0057] 2. Under the strength constraint of the matrix elastic rod material, compared with the high-rigidity rhombus lattice metamaterial structure, the overall buckling bearing strength of the layered array chiral metamaterial structure proposed in this embodiment is increased by 3 times, and the elastic energy storage density is increased by 5 times; compared with the high-rigidity octahedral lattice metamaterial structure, the overall buckling bearing strength of the layered array chiral metamaterial structure proposed in this embodiment is increased by more than 15 times, and the elastic energy storage density is increased by more than 20 times; compared with the tensile overall structure, the performance proposed in this embodiment is improved by more than 100 times.

[0058] The analysis of Example 1 shows that the diamond lattice configuration exhibits superior performance. Therefore, in Example 2, this embodiment designed a diamond lattice metamaterial structure composed of steel springs for comparison with a two-dimensional single-layer chiral metamaterial structure. The springs were molded with rectangular cross-sections. Steel springs have high environmental adaptability, mature manufacturing processes, and can maintain excellent elastic deformation recovery even under large deformations.

[0059] In Example 2, the spring has an outer diameter of 6 mm, an inner diameter of 3.2 mm, and a length of 30 mm. The performance comparison method is the same as in Example 1. The performance curve calculated using the nonlinear finite element method is as follows: Figure 10 As shown. The strength of the spring material is σ v =2.75GPa. Simulation results show that compared with the high-density diamond lattice structure, the chiral superstructure proposed in this embodiment can increase the overall buckling bearing strength by more than 3 times and the energy storage density by more than 5 times.

[0060] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A metamaterial structure based on independent chiral twist units, characterized in that: It includes a plurality of metamaterial cells, each of which is distributed in a three-dimensional skeleton configuration and is connected to form a spatial skeleton of a polyhedron structure; The metamaterial cell includes two mirror-symmetrical chiral units; the chiral unit includes two torus and a plurality of elastic rods, the two torus are coaxially spaced apart, and the elastic rods are periodically distributed between the two torus along the circumference of the torus; In the same chiral unit, when the chiral unit has no external load, the elastic rods are in an inclined state, and the inclination direction and inclination angle of each elastic rod are the same; The two mirror-symmetrical chiral units share one annular surface, or a pair of annular surfaces in the two mirror-symmetrical chiral units are coaxially fixedly connected.

2. The metamaterial structure based on independent chiral twisting units according to claim 1, characterized in that: The nodes of the space skeleton are block structures.

3. The metamaterial structure based on independent chiral twisting units according to claim 1 or 2, characterized in that: In the same chiral unit: The first end of the elastic rod is fixedly connected to one of the annular surfaces, and the distance between the center of the first end of the elastic rod and the center of the corresponding annular surface is a first pitch circle radius R1; The second end of the elastic rod is fixedly connected to another annular surface, and the distance between the center of the second end of the elastic rod and the center of the corresponding annular surface is a second pitch circle radius R2; Wherein, R1=R2=R, and R is the installation pitch radius of the elastic rod between the two annular surfaces.

4. The metamaterial structure based on independent chiral twisting units according to claim 3, characterized in that: In the same chiral unit, the distance between the two ring surfaces is h0, and h0≈4R~6R.

5. The metamaterial structure based on independent chiral twisting units according to claim 1 or 2, characterized in that: The elastic rod is a cylindrical structure that can withstand large deformations such as compression, bending and torsion, including but not limited to soft rubber rods, coil springs, steel wire ropes, carbon nanotubes, and fiber-reinforced rods.

6. The metamaterial structure based on independent chiral twisting units according to claim 1 or 2, characterized in that: In the same chiral unit, the distance between two adjacent elastic rods is greater than or equal to the diameter of the elastic rod.

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